The invention relates to an arrangement for the regulation by fluid means of the height of a liquid level comprising a fluid pick-up device and a two-phase outlet nozzle; such arrangement is particularly suitable for the regulation and removal of condensate from the regeneration heaters of steam turbines.
Arrangements now in use for the removal of condensate and of the regulation of liquid levels are distinguished according to the physical principle employed for obtaining information about the height of the liquid level in the regulated system. The oldest arrangements employ different types of float pick-up devices which transform information as to the height of the liquid level to a mechanical value of the position of the float. In the simplest embodiments of the regulating circuit for small throughflowing amounts of the removed liquid medium, for instance a condensate, it is thus possible directly to control the degree of opening or lift of a regulating valve.
Another simple principle for detecting the height of a liquid level is based on measuring the variations of pressure of a suitable gas passing through a tube submerged in the liquid in a vessel, the gas freely bubbling through the open end of the tube and through the liquid content of the vessel.
In one present practice for detecting the height of the level of a liquid, an electric feeler providing a current or voltage output signal is used. The fluidic principle utilizing changes of dynamic pressure due to the deceleration of a turbulent liquid jet flowing from a transmitting nozzle through a liquid layer above the pick-up nozzle is also used.
All these arrangements have some drawbacks. A common drawback of the three first mentioned arrangements is the low power of the output signal of pick-up devices, such power being insufficient for a direct control of regulating valves for removal of, for instance condensates. A consequence of the necessity of the amplification of the signals provided by these pick-up devices is the increasing complexity of the regulating feedback loop; this results mostly in an insufficiently quick dynamic response of such a circuit to a sudden change of the liquid level. For instance, in the case of a regenerator heater, there results an overstepping of permissible levels of failure, and the removal from operation of the heater from operation due to its breakdown.
A fluidic pick-up device for detecting liquid level provides a hydraulic output of sufficient power for the direct control of hydraulic servo devices for controlling regulating valves; however, the mixture of liquid, vapor and non-condensing gas causes, with a direct interconnection of the fluidic pick-up device and the hydraulic servo device via a longer conduit, oscillations of the control pressure and a discontinuous behavior of the circuit. Another serious drawback for the production of a circuit with quick dynamic response is the generation of a water shock or hammer, which occurs upon a sudden stoppage of a liquid in a long connecting conduit for the removal of the condensate by a quick closing of the regulating valve.